Electron-discharge-device circuits



J. c. SCHELLENG.

ELECTRON DISCHARGE DEVICE CIRCUITS. APPLICATION FILED MAY 11. 1921.

1,437,021, Patented Nov. 28,1922.

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JOHN C. SCHELLENG, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTERN ELEC TRIC CGMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF I I7.

YORK,

ELECTRON-DISCHARGE-DEVICE CIRCUITS.

Application filed May 11,

To all whom it may concern:

Be it known that I, JOHN C. SCHELLENG, a citizen of the United States, residing at East Orange, in the county of Essex, State of New Jersey, have invented certain new and useful Improvements in Electron-Discharge-Device Circuits, of which the following is a full, clear concise. and exact description.

This invention relates to means for pre venting vacuum tube systems from generating undesired oscillations. It is particularly applicable in the case of radio transmission systems utilizing electron discharge devices having plate, grid and filament electrodes for transmitting electromagnetic waves of hi h power.

n such vacuum tube systems, especially systems comprising a plurality of high power tubes in parallel, troublesome oscillations of undesired frequencies oftenoccur. In many instances these oscillations are of a frequency much higher than the frequencies normally used in signaling. These undesired oscillations often result in failure to operate at the proper frequency or in the capricious alternation of the frequency from one value to another, particularly during modulation. In some cases these exceedingly high frequenc oscillations manifest themselves by perio ic or irregular variations ,or phenomena which occur at lower frequencies or irregular periods respectively. In certain cases waves or impulses occur of such frequencies as to produceaudible sounds, which are especially objectionable. These high frequency waves may cause excessive differences of potential between certain closely placed parts of the apparatus. In some instances it has been supposed that the undesired oscillations were set up as a result of a cyclic transfer of energy through several vacuum tubes of a parallel group or of a closely related nonpa'rallel group. Among the most plausible of the theories advanced for the production of such oscillations-is that two tubes or two groups of tubes substantially equal in number cooperate to pro duce an oscillation circuit. By way of illustration, assume two tubes connected in parallel. The lead connecting their grids has a small inductance and the lead connecting their plates has a small inductance. Each tube has a grid-plate capacity, a grid-fila- 1921. Serial No. 468,739.

desired oscillations, their presence is detrie mental and the principal object of this invention is to provide means for their suppressl'on or reduction.

It has been found that the parasitic oscillations are stopped by the introduction of a small inductance coil in the individual electrode circuits of several vacuum tubes in a parallel or other system. It may be sufiicient to lace such inductance coils in the circuits of ess than the whole number of tubes of a group.

Preferably the inductance coils are located in the plate circuits of the several tubes. In the case of 50-watt tubes in parallel for radio transmission it has been found suflicient to use an inductance having a value of the order of 10 microhenr-ies. Larger inductances may be used in tubes which normally handle currents of low frequencies such as speech frequencies. The means described for preventing the production of undesired or parasitic oscillations is useful in amplifying and modulating, as well as in oscillating, systems of vacuum tubes, and .hence the invention in a broad aspect is not limited in applicability to vacuum tubes utilized for any particular purpose.

The invention is described with more particularity in connection with the accompanying drawings, wherein is illustrated a known form of radio transmission system having the elements constituting the invention embodied therein.

The drawings are acircuit diagram of the radio transmitter, which comprises a high frequency oscillating system 0, a variable impedance or modulating system V, an amplifying system A, and a source S of signaling waves or impulses. The oscillating system 0 comprises several vacuum tubes 1 ment circuits in parallel. In the plate circuit is included a coil 2 coupled to a coil 3 in an antenna 4. In the grid circuit is included a feed back coil 5 coupled to another coil 6 in the antenna circuit. A variometer 7 serves to tune the antenna. Condensers 8 and 9 serve to prevent the flow of direct current through their respective circuits but they are of such magnitude as to offer a negligible impedance to currents of the frequencies which the oscillator O is intended to roduce.

n order to signal, the oscillations produced by theo'scillator 0 must be modulated or' varied in amplitude or otherwise by means of signaling waves or impulses; The source S of signaling waves or impulses is illustrated in the alternative as being either a microphone circuit 10 or a buzzer circuit 11, either of which may be energized by means of the switchv 12. Waves or impulses produced by the source S are impressed through the transformer 13 on the amplifying tube 14 of the amplifying system A The amplified waves are impressed by means I of transformer '14 upon the input circuit'of the variable impedance vacuum tube system V which comprises several tubes 15' having tlllleilr plate, grid and filament circuits in ra e. plate current supply through a speech frequency choke coil 16 with the result that when the impedance of the system V is varied in accordance with signaling waves or impulses, the current flow through. the system 0 is caused to vary in the opposite sense as the current flow in the system V.

A high frequency choke coil 16 serves to offer a high lmpedance to oscillations of the frequency of those normally generated by the system 0. The arrangement so far described constitutes a radio transmitter wherein the'high frequency oscillations are modulated in accordance with what is known as the. constant current system of modulation.

For transmitting large amounts of ower it is necessary that the tubes 1 and 15 s ould be able to cooperate to produce alarge amount of modulated high frequency energy in the antenna circuit. The power capacity of each individual tube must therefore be considerable, for example, 50 watts or more. As described in the preceding portion of this specification undesired oscillations often manifest themselves in'systems of this kind with the result that the operation is interferred with.

To correct this defect the inductance coils 17 are included in the plate circuits of the various tubes as illustrated. In practice it has been found possible to construct these coils in a very simple manner, viz., by winding ten or twenty turns, more or less, of in- The systems 0 and V receive t eir" an undesired manner with one or moreof' the other tubes to form a cyclic path or channel through which high frequency energy is transferred, or if it tends to oscillate of itself, it may be advisable to include. the choke. coil in its plate circuit as illustrated. The system of tubes V may be considered merely as being a variable impedance system or it may be considered as being an amplifying system for impressing upon the plate circuits of the tubes 1 the waves received from the plate circuit of the tube 14. Where undesired oscillations occur as a result of a cyclic transfer of energy through several tubes it may be possible to prevent these by including inductances 17 in the circuits of one or more but not of all of the tubes. Hence from a broad aspect this invention is not limited to the use of the 1nductances 17 in the circuits of every tube in a particular system or every tube of a parallel grou The use of the words plate, grid, and lament in describing. the elements of discharge devices are to be understood in their generic sense as referring to anode, control, and cathode electrodes of any form or construction. 7

Having described the invention in detail the various novel and patentable features and combinations believed to be inherent in the invention are set forth in the appended claims.

What is claimed is: y

1. In a system comprising a number of discharge devices having their corresponding electrode circuits connected in parallel, a choking inductance in a number of the corresponding electrodecircuits.

2. In a system comprising a number of discharge devices each having plate, grid, and filament electrode circuits, their corresponding circuits being in parallel, separate choking inductances individual to said cor responding electrode circuits respectively.

3. In a system comprising a number of discharge devices having plate, grid and filament electrodes, corresponding electrode circuits therefor in parallel, and a choking inductance in one of said corresponding electrode circuits.

4. In a system comprising a number of discharge deviceshaving plate, grid and filament electrodes, electrode circuits therefor in parallel including plate electrode circuits, and a choking inductance in each of a number of the corresponding plate electrode circuits.

5. In a system comprising a number of Learner discharge devices having plate, grid and filament electrodes, corresponding electrode circuits -therefor in parallel including plate electrode circuits, and choking inductances individual to each of said corresponding electrode circuits.

6. In a system comprising a number of discharge devices having plate, control and filament electrodes, corresponding electrode circuits therefor in parallel including plate electrode circuits, and a choking inductance in one of said plate electrode circuits.

7. In an oscillation generator a thermionic vacuum discharge device having appropriate circuits and appropriate power sources connected thereto for the generation of oscilla tions, a plate circuit for said vacuum device,

said plate circuit including an inductance of such a small value as to prevent the generation of parasitic oscillations of a materially higher frequency than the desired oscillations, but not to materially interfere with the generation of the desired oscillations.

8. In an amplifying device a space discharge tube having appropriate circuits and appropriate power sources connected thereto for the amplification of electrical waves or impulses, a plate circuit for said tube, said plate circuit including a small inductance of a value suitable to prevent the generation of parasitic oscillations of a materially higher frequency than the waves or impulses to be amplified, but not to materially interfere with the amplification of the waves or impulses.

9. In a vacuum tube system a plurality of space. discharge tubes and means for pre venting generation of undesired oscillations due to the conductive connections or the close proximity of the tubes or both, comprising an inductance individual to the plate circuit of one of the tubes of a value suitable to prevent the generation of undesired oscillations, but not to prevent the normal functioning of said tubes.

10. A vacuum tube repeater having a plate circuit, a principal inductance in said plate circuit, and an auxiliary inductance having a value of the order of 10 microhenries also included in said plate circuit for preventing the production of parasitic oscillations at ultraradio frequencies.

11. A constant current modulating system comprising a high frequency tube and a variable impedance low frequency tube, each of said tubes having a space current circuit and an auxiliary inductance in the space current circuit of one of said tubes for preventing the production of parasistic oscillations.

12. In a radio transmitter comprising a plurality of high power tubes having their corresponding circuits connectedin parallel for the generation and transmission of high power oscillations, an auxiliary inductance individual to the plate circuit of one ofsaid tubes. i

In witness whereof, I hereunto subscribe my name this 10th day of May, A. D., 1921.

JOHN C. SCHELLENG. 

